Acoustic determination of piston position in a modular dynamics tester displacement pump and methods to provide estimates of fluid flow rate

Abstract

A method for determining a piston position in a downhole tool, having steps of providing a transducer in the downhole tool, wherein the tool has a piston used to create a vacuum for the downhole tool, providing a transducer tone burst to provide acoustic energy toward the piston, reflecting the transducer tone burst by a surface of the piston, receiving the transducer tone burst at a receiver, calculating time of flight for the transducer tone burst and determining the piston position in the downhole tool based upon the calculated time of flight of the transducer tone burst.

What is claimed is: 
     
       1. A method for determining a piston position in a positive displacement pump of a downhole tool, comprising:
 providing a transducer in the downhole tool, wherein the positive displacement pump has a piston used to create a vacuum for the downhole tool; 
 contacting a surface of the piston with a fluid disposed within a fluid chamber of the positive displacement pump; 
 providing a transducer tone burst of acoustic energy across the fluid chamber and toward the surface of the piston; 
 reflecting the transducer tone burst by the surface of the piston; 
 receiving the transducer tone burst at a receiver; 
 calculating time of flight for the transducer tone burst; and 
 determining the piston position in the positive displacement pump based upon the calculated time of flight of the transducer tone burst. 
 
     
     
       2. The method according the  claim 1 , wherein the transducer tone burst is at a frequency of 4 MHz. 
     
     
       3. The method according to  claim 1 , wherein the receiving the transducer tone burst at the receiver is performed at the transducer. 
     
     
       4. The method according to  claim 1 , further comprising:
 controlling a speed of the positive displacement pump associated with the piston. 
 
     
     
       5. The method according to  claim 1 , further comprising:
 estimating a flow rate of a reservoir fluid. 
 
     
     
       6. The method according to  claim 1 , wherein the providing the transducer tone burst of acoustic energy toward the surface of the piston is accomplished through a fluid. 
     
     
       7. The method according to  claim 6 , wherein the fluid is a downhole fluid. 
     
     
       8. The method according to  claim 1 , wherein the calculating the time of flight for the transducer tone burst is performed through a correlation of an independent measurement of the speed of sound in a fluid obtained in an apparatus separate from the downhole tool. 
     
     
       9. The method according to  claim 1 , wherein the calculating the time of flight for the transducer tone burst is performed through an in situ measurement of the speed of sound of fluid contained in a hydraulic mechanism of the positive displacement pump. 
     
     
       10. A system for determining a position of a piston in a positive displacement pump of a downhole tool, comprising:
 a cylinder configured to contain a fluid pumped by the positive displacement pump; 
 a cylinder head attached to one end of the cylinder; 
 a piston placed within the cylinder, the piston movable between a first top position to a second bottom position, wherein the cylinder, the cylinder head and the piston define a volume; and 
 a transducer and associated electronics positioned adjacent to the cylinder wherein the transducer is configured to produce a transducer tone burst of acoustic energy across the cylinder and toward a surface of the piston, wherein the transducer and associated electronics are configured to calculate a position of the piston in the volume through time of flight calculations. 
 
     
     
       11. The system according to  claim 10 , further comprising:
 a pump speed controller, wherein the pump speed controller is controlled through actuation of the associated electronics. 
 
     
     
       12. An article of manufacture, comprising:
 a computer readable medium that is adapted to perform a method of determining a piston position in a positive displacement pump of a downhole tool, the computer readable medium adapted to be used in conjunction with a nonvolatile memory such that the computer may execute the method comprising: 
 providing a transducer in the downhole tool, wherein the positive displacement pump has a piston used to create a vacuum for the downhole tool; 
 providing a transducer tone burst of acoustic energy across a fluid chamber of the positive displacement pump and toward a surface of the piston; 
 reflecting the transducer tone burst by the surface of the piston; 
 receiving the transducer tone burst at a receiver; 
 calculating time of flight for the transducer tone burst; and 
 determining the piston position in the positive displacement pump based upon the calculated time of flight of the transducer tone burst. 
 
     
     
       13. The article of manufacture according the  claim 12 , wherein the method performed produces a transducer tone burst at a frequency of 4 MHz. 
     
     
       14. The article of manufacture according to  claim 12 , wherein the method performed including receiving the transducer tone burst at the receiver is performed at the transducer. 
     
     
       15. The article of manufacture according to  claim 12 , wherein the method performed further comprises controlling a speed of the positive displacement pump associated with the piston. 
     
     
       16. The article of manufacture according to  claim 12 , wherein the method performed further comprises estimating a flow rate of a reservoir fluid. 
     
     
       17. The article of manufacture according to  claim 12 , wherein the providing the transducer tone burst of acoustic energy toward the surface of the piston is accomplished through a fluid. 
     
     
       18. The article of manufacture according the  claim 12 , wherein the method performed further comprises contacting the surface of the piston with a fluid disposed within the fluid chamber.